1. Field of the Invention
The present invention relates generally to anti-friction bearings for linear motion and more specifically to linear motion ball bearings disposed upon a pair of pre-aligned shafts which are coupled together.
2. Description of the Prior Art
Representative examples of linear motion ball bearings are described in U.S. Pat. Nos. 2,628,135, 3,545,826 and 4,334,716 which are assigned to the assignee of the present invention. Illustratively, U.S. Pat. No. 3,545,826 describes a self-aligning linear motion ball bearing in which a ball retainer having oblong raceways is disposed around a shaft. The oblong raceways include load bearing and load free portions and are substantially filled with balls. A load bearing plate is located in that portion of each of the raceways in which the balls directly contact the shaft upon which the bearing is mounted. U.S. Pat. No. 4,334,716 is directed towards a linear motion ball bearing of the "open type" in which the ball bearing cooperates with a shaft supported along its length. The ball retainer of the "open type" linear motion ball bearing is similar to that described in U.S. Pat. No. 3,545,826 except that it has a longitudinal section removed from its outer surface in order to accommodate the shaft support member.
Whenever a rotational force or torque is applied to such bearings, the bearings do not resist rotation about their shaft. However, in some applications even a small amount of rotation is undesirable. Resorting to the use of two parallel shafts as supports for the bearings may not be an acceptable solution because of the substantial difficulty in locating the shafts parallel to and accurately spaced from each other so as to enable the shafts and bearings to function properly together. More particularly, when linear motion ball bearings are used to support a moving work or support table, two parallel shafts are generally required to give the table stability. One of the installation problems includes mounting the shafts exactly parallel within close limits as well as having their centerlines accurately spaced apart. Many times, the user has difficultly in achieving the accuracy required. Accordingly, there is a need for shafts that are fixedly coupled together and which can support linear motion bearings.
One of the objects of this invention is to provide two pre-aligned and securedly coupled shafts thereby eliminating an installation problem. Another object is to provide two shafts fixed together, with or without spacers between them, so as to form a more rigid beam structure which is capable of resisting deflection when the shafts are supported at their ends.
Another object is to have two prealigned shafts coupled together with a special shaped spacer wherein the structure can be mounted on a flat surface thereby supporting the shafts along their full length instead of at the ends, in order to have even a more rigid support and better ability to resist deflection.